5.15-stable review patch. If anyone has any objections, please let me know.
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From: Serge Semin fancer.lancer@gmail.com
commit e1a9ae45736989c972a8d1c151bc390678ae6205 upstream.
max_mapnr variable is utilized in the pfn_valid() method in order to determine the upper PFN space boundary. Having it uninitialized effectively makes any PFN passed to that method invalid. That in its turn causes the kernel mm-subsystem occasion malfunctions even after the max_mapnr variable is actually properly updated. For instance, pfn_valid() is called in the init_unavailable_range() method in the framework of the calls-chain on MIPS: setup_arch() +-> paging_init() +-> free_area_init() +-> memmap_init() +-> memmap_init_zone_range() +-> init_unavailable_range()
Since pfn_valid() always returns "false" value before max_mapnr is initialized in the mem_init() method, any flatmem page-holes will be left in the poisoned/uninitialized state including the IO-memory pages. Thus any further attempts to map/remap the IO-memory by using MMU may fail. In particular it happened in my case on attempt to map the SRAM region. The kernel bootup procedure just crashed on the unhandled unaligned access bug raised in the __update_cache() method:
Unhandled kernel unaligned access[#1]: CPU: 0 PID: 1 Comm: swapper/0 Not tainted 6.7.0-rc1-XXX-dirty #2056 ... Call Trace: [<8011ef9c>] __update_cache+0x88/0x1bc [<80385944>] ioremap_page_range+0x110/0x2a4 [<80126948>] ioremap_prot+0x17c/0x1f4 [<80711b80>] __devm_ioremap+0x8c/0x120 [<80711e0c>] __devm_ioremap_resource+0xf4/0x218 [<808bf244>] sram_probe+0x4f4/0x930 [<80889d20>] platform_probe+0x68/0xec ...
Let's fix the problem by initializing the max_mapnr variable as soon as the required data is available. In particular it can be done right in the paging_init() method before free_area_init() is called since all the PFN zone boundaries have already been calculated by that time.
Cc: stable@vger.kernel.org Signed-off-by: Serge Semin fancer.lancer@gmail.com Signed-off-by: Thomas Bogendoerfer tsbogend@alpha.franken.de Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/mips/mm/init.c | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-)
--- a/arch/mips/mm/init.c +++ b/arch/mips/mm/init.c @@ -417,7 +417,12 @@ void __init paging_init(void) (highend_pfn - max_low_pfn) << (PAGE_SHIFT - 10)); max_zone_pfns[ZONE_HIGHMEM] = max_low_pfn; } + + max_mapnr = highend_pfn ? highend_pfn : max_low_pfn; +#else + max_mapnr = max_low_pfn; #endif + high_memory = (void *) __va(max_low_pfn << PAGE_SHIFT);
free_area_init(max_zone_pfns); } @@ -453,13 +458,6 @@ void __init mem_init(void) */ BUILD_BUG_ON(IS_ENABLED(CONFIG_32BIT) && (_PFN_SHIFT > PAGE_SHIFT));
-#ifdef CONFIG_HIGHMEM - max_mapnr = highend_pfn ? highend_pfn : max_low_pfn; -#else - max_mapnr = max_low_pfn; -#endif - high_memory = (void *) __va(max_low_pfn << PAGE_SHIFT); - maar_init(); memblock_free_all(); setup_zero_pages(); /* Setup zeroed pages. */